Controlled leakage face type shaft seal

ABSTRACT

A hydrostatic seal wherein a shaft rotates in a stationary pump housing and carries a first sealing ring defining an annular gap with an axially movable second sealing ring in the housing. The gap permits controlled leakage of fluid from a pressure chamber into a low-pressure area adjacent to the periphery of the shaft. The second ring is urged toward the first ring by one or more weak springs, and the rings are surrounded by annular permanent magnets having similar poles adjacent to each other so that the magnets tend to move the second ring away from the first ring. The magnets become effective when the pressure of fluid in the chamber decreases to such an extent that the springs and/or gravity could reduce the width of the gap to zero. The magnets are encapsulated to avoid corrosion on contact with fluid in the pressure chamber.

United States Patent] [1 1 [111 3,869,135 Diederich Mar. 4, 1975 1CONTROLLED LEAKAGE FACE TYPE 3,137,237 6/1964 Zagar et a1 277/80 SHAFTSEAL [75] Inventor: Herbert Diederich,

Frankenthal/Pfalz, Germany [73] Assignee: KSB Kernkraftwerkspumen GmbH,

Frankenthal, Germany [22] Filed: Mar. 25, 1974 [21] Appl. No.: 454,411

[30] Foreign Application Priority Data Mar. 27, 1973 Germany 2315190[52] 11.5. CI. 277/80 [51] Int. Cl. Fl6j 9/00 [58] Field of Search277l80-96 [56] References Cited UNITED STATES PATENTS 2,843,403 7/1958Stevenson 277/80 2,883,212 4/1959 Laser 277/80 2,913,289 11/1959Stevenson... 277/80 2,996,162 8/1961 Lehde. 277/80 3,050,319 8/1962Colby 277/80 Primary E.\'aminerRichard E. Aegerter AssistantExaminerRobert J. Smith Attorney, Agent, or Fir/71Michael S. Striker[57] ABSTRACT A hydrostatic seal wherein a shaft rotates in a stationarypump housing and carries a first sealing ring defining an annular gapwith an axially movable second sealing ring in the housing, The gappermits controlled leakage of fluid from a pressure chamber into alowpressure area adjacent to the periphery of the shaft. The second ringis urged toward the first ring by one or more weak springs, and therings are surrounded by annular permanent magnets having similar polesadja cent to each other so that the magnets tend to move the second ringaway from the first ring. The magnets become effective when the pressureof fluid in the chamber decreases to such an extent that the springsand/or gravity could reduce the width of the gap to zero. The magnetsare encapsulated to avoid corrosion on contact with fluid in thepressure chamber.

10 Claims, 1 Drawing; Figure .i. CONTROLLED LEAKAGE FACE TYPE SHAFT SEALBACKGROUND OF THE INVENTION The-present invention relates to hydrostaticseals in general, and more particuarly to fluid seal assemblies of thetype known as controlled leakage face type shaft seals. Such seals canbe used to permit controlled leakage of fluid from a pressure chamberinto a low pressure area, for example, in a centrifugal pump which isinstalled in a nuclear reactor plant. Reference may be had to GermanPrinted Publication No. 1,650,061 of Sept. 4, 1969 and to the commonlyowned copending application Ser. No. 353,133 filed Apr. 20, 1973 byPeter Stech.

The hydraulic forces which are necessary in a shaft seal to maintain thewidth of the gap between a first sealing ring which rotates with theshaft and a second sealing ring which is axially movable in but cannotrotate with respect to the housing depend on the difference betweenfluid pressure in the pressure chamber and that in a low-pressure areaof the pump. If the difference is small or decreases to zero, the widthof the gap between the sealing rings becomes unpredictable and normallytends to decrease so that the sealing rings actually touch each other.Such contact between the sealing rings will take place if the axiallymovable ring is located at a level above the other ring. A reduction ofthe width of the gap to zero is undesirable, especially during startingof the pump in a nuclear reactor plant, because the wear on the surfacesbounding the gap is very high. Attempts to avoid contact between thesealing rings during starting include the provision of means for raisingthe pressure of fluid in the high-pressure chamber before the shaftbegins to rotate. This presents serious problems as concerns the energyand space requirements of the pump.

It was further proposed to employ hydraulic or mechanical springs whichtend to move the sealing rings of a shaft seal away from each other soas to avoid a reduction of the width of the gap to zero when the fluidpressure in the high-pressure chamber decreases. Such proposal exhibitsthe drawback that the pump must be I provided with a hydrodynamic sealdownstream of the gap so as to seal the low-pressure area from theatmosphere while the pump is idle.

SUMMARY OF THE INVENTION An object of the invention is to provide anovel and improved shaft seal wherein the sealing rings are held out ofcontact with each other during each stage of operation and in eachcondition of the machine or apparatus which embodies the seal.

Another object of the invention is to provide a shaft seal with noveland improved means for maintaining the sealing rings out of contact witheach other when the difference between the pressure fluid in thepressure chamber and the pressure of fluid in the lowpressure areadecreases to a value at which the fluid in the pressure chamber would beunable to hold the axially movable sealing ring out of contact with theother sealing ring.

A further object of the invention is to provide novel and improvedsealing rings for use in controlled leakage face type shaft seals.

The invention is embodied in a fluid seal arrangement which comprises ashaft member, a housing member which spacedly surrounds the shaft memberand defines therewith a fluid-containing pressure chamber and alow-pressure area adjacent to the peripheray of the shaft member, meansfor rotating one of the members (preferably the shaft member) about theaxis of the shaft member, first and second sealing rings which arelocated in the pressure chamber and are respectively secured to thehousing member and shaft member, means for guiding one of the sealingrings for movement axially of the shaft member, front surfaces providedon the two sealing rings and defining an annular gap for the leakage offluid from the pressure chamber into the low-pressure area, a rearsurface provided on the one sealing ring and facing away from therespective front surface, the fluid which is contained in the pressurechamber acting against the front and rear surfaces and therebymaintaining the width of the annular gap within a predetermined range aslong as the pressure of fluid in the pressure chamber exceeds apreselected value, and first and second magnets respectively provided onthe first and second rings and having similar poles adjacent to eachother to urge the one ring away from the other ring and to thus preventexcessive reduction of the width of the gap when the pressure of fluid.in the pressure chamber is less than the preselected value.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved shaft seal itself, however, both as to its construction and itsmode of operation, together with additonal features and advantagesthereof, will be best understood upon perusal of the following detaileddescription of certain specific embodiments with reference to theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE is a fragmentaryaxial sectional view of a controlled leakage face type shaft seal whichembodies the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The drawing shows a controlledleakage face type shaft seal wherein a pump shaft 4' rotates in a pumphousing 2. The housing 2 has a main portion 2a which defines with theshaft 4 a fluid-containing pressure chamber 6, and a cylindrical secondportion 2b which defines with the shaft 4 a low-pressure area 7.

The means for permitting a controlled leakage of fluid from the chamber6 into the low-pressure area 7 comprises two sealing rings 1 and 3. Thering 3 is secured to and rotates with the shaft 4 (for' example, the

coupling between the ring 3 and shaft 4 may be of the type as disclosedand shown in the commonly owned copending application Ser. No. 353,133filed Apr. 20, 1973 by Peter Stech) and defines with the ring 1 anannular gap 8 extending between the chamber 6 and lowpressure area 7. Agasket 9 is interposed between the ring 3 and shaft 4, and a similargasket 10 is installed between the housing portion 2b and ring 1. Thelatter is movable axially of the shaft 4 and is biased toward the ring 3by one or more helical springs 11. The ring 1 is held against rotatingin the housing 2, preferably in a manner as disclosed in theaforementioned copending application of Stech. Fluid in the chamber 6acts upon the front and rear surfaces la, lb of the ring 1 to normallyinsure that the gap 8 allows for controlled leakage of fluid from thechamber 6 into the low-pressure area 7. The front surface 1a is locatedoppositea radially extending front surface 3a of the rotary ring 3.

In accordance with a feature of the invention, the ring 1 is providedwith a first permanent magnet 5 which faces a second permanent magnet 12on the ring 3. The adjacent poles of the magnets 5, 12 are similar and,therefore, the magnets tend to repel each other and to increase thewidth of the gap 8 between the front surface la of the ring 1 and thefront surface 3a of the ring 3. The magnets 5 and 12 become effective assoon as the magnitude of hydraulic sealing forces'decreases to such anextent that the spring or springs 11 (and/or the force of gravity if thepump is mounted in an upright position with the ring 1 located at alevel above the ring 3) would be likely to reduce the width of the gap 8to zero. v

The magnets 5 and 12 are preferably annular and are preferablyencapsulated in suitable sheaths or casings 105, 112 (indicated byphantom lines) to avoid corrosion in response to contact with hydraulicfluid in the chamber 6.

The purpose of the spring or springs 11 is to prevent excessive wideningof the gap 8 when the pressure in the chamber 9 decreases below apreselected valve. These springs oppose the tendency of the magnets 5,12 to increase the width of the gap 8 when the pump is idle and thepressure in the chamber 6 is low. The hydrostatic forces which act onthe ring 1 when the pump is in use are large enough to establish anoptimum width of the gap 8 irrespective of the tendency of magnets 5 and12 to move the ring 1 axially and away from the ring 3. Thus, therepelling force of the magnets 5, 12 is negligible when the fluid in thechamber 6 is maintained at normal operating pressure. However, therepelling force of the magnets 5, 12 should suffice to overcome thetendency of one or more O-rings (each of the gaskets 9, 10 may includean O-rin g) to move the ring 1 toward the ring 3. The repelling force ofthe magnets 5, 12 decreases in response to increasing width of the gap8, and such force decreases at a rate which is much higher than therateof increase in the distance between the neighboring poles of themagnets. The spring or springs 11 insure that the width of the gap 8does not increase beyond a predetermined value when the pressure offluid in the chamber 6 decreases so that the magnets 5 and 12 can pushthe ring 1 away from the ring 3.

The drawing shows that the axial length of the magnets 5, 12 equals orapproximates the axial length of the respective rings 1, 3, that theright-hand surface 5a of the magnet 5 is flush with the outermostportion of the front surface la, and that the left-hand surface 12a ofthe magnet 12 is flush with the outer portion of the front surface 30.The surface la has portions which are inclined with respect to thesurface 3a so that the width of the corresponding portions of the gap 8decreases in a direction toward the periphery of the shaft 4.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featureswhich fairly constitute essential characteristics of the generic andspecific aspects of my contriburion to the art and, therefore, suchadaptations should and are intended to be comprehended within themeaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. In a fluid seal arrangement, the combination of a shaft member; ahousinng member spacedly surrounding said shaft member and definingtherewith a fluidcontaining pressure chamber and a low-pressure areaadjacent to the periphery of said shaft member, one of said membersbeing rotatable about the axis of said shaft member; first and secondsealing rings coaxial with said shaft member, located in said chamberand respectively secured to said housing member and said shaft member,one of said rings being movable axially of said shaft member and saidrings having neighboring front surfaces defining an annular gap for theleakage of fluid from said chamber into said area, said one ring furtherhaving a rear surface facing away from the respective front surface andbeing exposed to the pressure of fluid in said chamber whereby the fluidcontained in said chamber and acting on said surfaces maintains thewidth of said gap within a predetermined range as long as the fluidpressure in said chamber exceeds a preselected value; and first andsecond magnets respectively provided on said first and second rings andhaving similar poles adjacent to-each other to urge said one ring awayfrom the other'of said rings and to thus prevent excessive reduction ofthe width of said gap when the pressure of fluid in said chamber is lessthan said preselected value.

2. The combination of claim 1, further comprising means for biasing saidone ring axially toward said other ring.

3. The combination of claim 1, wherein each of said magnets includes anannular permanent magnet.

4. The combination of claim 3, wherein said annular magnets surround therespective rings.

5. The combination of claim 3, further comprising means for sealing saidmagnets against contact with the fluid in said chamber.

6. The combination of claim 1, wherein each of said magnets has asurface flush with the front surface of the respective ring.

7. The combination of claim 1, wherein said magnets are located in saidchamber.

8. The combination of claim 1, wherein said one sealing ring is saidfirst ring and said one member is said shaft member.

9. The combination of claim 1, wherein at least a portion of one of saidfront surfaces is inclined with respect to the other of said frontsurfaces so that the width of the corresponding portion of said gapdecreases in a direction toward the periphery of said shaft member.

10. The combination of claim 1, wherein each of said magnets is anannular permanent magnet which surrounds the respective ring, the axiallength of each of said annular magnets being equal to or approximatingthe axial length of the respective rings.

1. In a fluid seal arrangement, the combination of a shaft member; ahousinng member spacedly surrounding said shaft member and definingtherewith a fluid-containing pressure chamber and a low-pressure areaadjacent to the periphery of said shaft member, one of said Membersbeing rotatable about the axis of said shaft member; first and secondsealing rings coaxial with said shaft member, located in said chamberand respectively secured to said housing member and said shaft member,one of said rings being movable axially of said shaft member and saidrings having neighboring front surfaces defining an annular gap for theleakage of fluid from said chamber into said area, said one ring furtherhaving a rear surface facing away from the respective front surface andbeing exposed to the pressure of fluid in said chamber whereby the fluidcontained in said chamber and acting on said surfaces maintains thewidth of said gap within a predetermined range as long as the fluidpressure in said chamber exceeds a preselected value; and first andsecond magnets respectively provided on said first and second rings andhaving similar poles adjacent to each other to urge said one ring awayfrom the other of said rings and to thus prevent excessive reduction ofthe width of said gap when the pressure of fluid in said chamber is lessthan said preselected value.
 2. The combination of claim 1, furthercomprising means for biasing said one ring axially toward said otherring.
 3. The combination of claim 1, wherein each of said magnetsincludes an annular permanent magnet.
 4. The combination of claim 3,wherein said annular magnets surround the respective rings.
 5. Thecombination of claim 3, further comprising means for sealing saidmagnets against contact with the fluid in said chamber.
 6. Thecombination of claim 1, wherein each of said magnets has a surface flushwith the front surface of the respective ring.
 7. The combination ofclaim 1, wherein said magnets are located in said chamber.
 8. Thecombination of claim 1, wherein said one sealing ring is said first ringand said one member is said shaft member.
 9. The combination of claim 1,wherein at least a portion of one of said front surfaces is inclinedwith respect to the other of said front surfaces so that the width ofthe corresponding portion of said gap decreases in a direction towardthe periphery of said shaft member.
 10. The combination of claim 1,wherein each of said magnets is an annular permanent magnet whichsurrounds the respective ring, the axial length of each of said annularmagnets being equal to or approximating the axial length of therespective rings.